1. Field of the Invention
The present invention relates to a signal output circuit and a semiconductor integrated circuit that are configured to output a signal from a first circuit that is driven based on a first reference signal to a second circuit that is driven based on a second reference signal.
2. Description of the Related Art
An IIL (integrated injection logic) circuit is a low-power logic circuit that is fabricated by a bipolar process. An IIL circuit can normally be integrated with an analog circuit by performing an analog process (e.g., see Japanese Laid-Open Patent Publication No. 2000-244301). In this case, a system may be configured in which an output signal of the IIL circuit controls the analog circuit. In such an integrated circuit, the output signal of the IIL circuit has to be input to the analog circuit.
FIGS. 4A and 4B are block diagrams illustrating exemplary configurations of integrated circuits. FIG. 4A shows an integrated circuit with a reference voltage V01 set to 0 V, and FIG. 4B shows an integrated circuit with a reference voltage V02 set to 5 V.
In these drawings, it is assumed that a first circuit 1 corresponds to an IIL circuit and a second circuit 2 corresponds to an analog circuit. In FIG. 4A, where the reference voltage V01 is set to 0 V, the first circuit 1 generates a signal based on the reference signal V01, and the signal generated at the first circuit 1 is supplied to the second circuit 2.
The second circuit 2 is an analog circuit that is controlled by the signal from the first circuit 1. In FIG. 4A where the reference voltage V01 is set to 0 V, the second circuit 2 is driven based on the reference voltage V01.
Similarly, in FIG. 4B where the reference voltage V02 is set to 5 V, the first circuit 1 and the second circuit 2 use the reference voltage V02 as a common reference voltage.
However, it is noted that a high-level output of an IIL circuit is normally 0.7 V and a low-level output of the IIL circuit is normally 0 V. On the other hand, a power supply voltage Vcc of an analog circuit is normally +5 V and the reference voltage of the analog circuit is normally −5 V. Therefore, when an integrated circuit is configured in the manner illustrated in FIGS. 4A and 4B, design alterations have to be made in at least one of the ILL circuit or the analog circuit.